Project Summary/Abstract. Postoperative cognitive dysfunction (POCD), the most common postoperative complication among geriatric patients and an important research area in the field of Geriatrics and Aging, is associated with substantially increased Alzheimer?s disease (AD) dementia, morbidity, and mortality as well as cost of care. However, the pathogenesis of POCD is still largely unknown, which impede the further studies into POCD. Consistent with the notion that blood CX3CR1+ monocytes and the mitochondria permeability transition pore component Cyclophilin D (CypD) in the brain regulate neuroinflammation and mitochondrial function, our published work and preliminary studies in mice showed that CypD and CX3CR1+ monocytes mediated anesthesia/surgery- and infection-induced cognitive impairment. In addition, CypD levels are higher in brain tissues of AD transgenic (Tg) and aged mice. Thus, the proposed research will assess the effects of anesthesia/surgery on toxicity, including the AD neuropathogenesis-associated changes (e.g., increased CypD levels, neuroinflammation, mitochondrial dysfunction, and neuronal dysfunction). Moreover, we will define a multifactorial model of POCD pathogenesis where the interaction of blood (anesthesia/surgery-induced increases in CX3CR1+ monocytes, the precipitating factor and insulting action) and brain [aging- or AD gene mutation-associated elevation of Cyclophilin D (CypD), the predisposing factor and gating regulation] is needed to cause POCD. The hypothesis of the proposed study is that anesthesia/surgery-induced increases in blood CX3CR1+ monocytes functionally interact with aging- and AD gene mutation-associated enhancement of brain CypD, leading to neuronal dysfunction and POCD-like behavior in mice. We will employ chemical and genetic tools through both neuroimmunology and behavioral approaches to accomplish three Specific Aims: (1) we will assess the effects of anesthesia/surgery on levels of blood CX3CR1+ monocytes and cytokines; brain- infiltrating CX3CR1+ monocytes, neuroinflammation, mitochondrial dysfunction, neuronal dysfunction, and behavior; (2) we will use Cx3cr1CreER/+;R26iDTR/+ and CypD knockout chimeric mice in which CX3CR1+ monocytes, microglia and CypD are depleted so we can assess the roles of blood CX3CR1+ monocytes and brain CypD on the anesthesia/surgery-induced changes; (3) we will determine the effects of a monoclonal antibody for the CX3CR1 ligand CX3CL1; and the protectors of mitochondria (WS635 and Vitamin K2) on the anesthesia/surgery-induced changes. We will include wild-type and adult (4 month-old) mice versus age matched AD Tg and aged (18 month-old) mice (with higher levels of CypD) while employing in vivo cell depletion, in vivo two-photon calcium imaging, Western blot, ELISA, immunohistochemistry, flow cytometry, and behavioral tests. This proposal aims to investigate an understudied topic in innovative systems by testing novel hypotheses, which would ultimately provide better postoperative outcomes for AD and geriatric patients, leading to the development of strategies to prevent AD.